Others here have made reference to the Eyewall Replacement Cycle. This is a natural evolution of the tropical cyclone as it cycles through periods of strengthening and weakening. The radar iamges we see show a "slice" of the atmosphere just above the surface of the earth. What is going on throughout the entire volume of the atmosphere is quite complex, though. What we see on radar is usually a response to other factors in the atmosphere - like dry air intrustion, and the weakening of an eye wall as winds weaken and spread out.

As we saw with Andrew, hurricanes can rapidly strengthen as well and produce winds at the surface even higher than what might be estimated from radar. Lots of research from people much smarter than myself continues to be done on how to best analyze and forecast these short-term changes.

--------------------"Let tomorrow worry about itself. Each day has enough trouble of its own."

You may wish to believe it that way, but it was really a combination of an eyewall replacement cycle and cooler waters just offshore that likely caused Dennis to weaken. Last year was somewhat of an abberation for tropical cyclone tornadoes, with so many from all of the storms; the number seen with this one so far (about 5-10) is more of a normal figure.

Winds that may translate down to the surface from upper levels (not downbursts here...but just the wind speed that is found at the lower levels in conjunction with the upper level winds) are generally going to be higher over water than over land due to frictional effects. There is much less friction over water than there is over land, leading to higher wind speeds. Friction can knock quite a bit off of a storm's intensity pretty quickly all by itself; the loss of the warm waters will serve to weaken the storm even further once it makes landfall. The combination of the two factors helped to see the quick change in structure and intensity once inland.

With the storm moving north, almost all of the convection, outflow, and light/moderate tropical rains is going to be found on the north side -- this holds true for just about every such tropical cyclone. The outer feeder bands are nothing out of the ordinary; while the dry slot to its east may not occur with every storm, it certainly is not an uncommon experience, either. Needless to say, Dennis was a pretty formidable storm at landfall, one which the Pensacola area will be cleaning up from for years to come. Category 2, category 3, category 4...it doesn't matter...the damage is still going to be very extensive.

Between 12 and 2 am we got a rain band and had torrential rain , lightning, and wind gusts to 50 mph and at times it seemed alot stronger gusts as it pounded the rain against my windows. Man it really brought bad horrible memories from last year being in the eye of both Frances and jeanne. Needless to say My nerves were shot all over again last night my heart really went out to those dealing with Dennis today. Thank God it wasn't as bad as it could have been

A: NWSMLB says it will not bring significant weather, but bears watching.
B: Thats 98L, may become a TD later tonight or Monday
C: Could also develop, but needs to move farther west before anything happens.

As for which has some potential for development...I think the answer is "D - All of the above". The way things have been going so far this year I think you could blow a smoke-ring from a cigar and have it develop. Starting to make me wonder why I have a cruise booked for....October...

Just a post from someone in Pensacola here. Pensacola got lucky on this one. The sudden jump northward at the last minute saved our butts. From just being out a little bit ago, nothing major is damaged. There are a few trees down and a few landed on some structures. Roads were passable (which was impossible with Ivan right after).

And I got extremely lucky and did not loose power durring the entire storm. I don't know how that happend, but quite a few places in town never lost power. I think maybe Ivan already cleared all the trees that were weak. So this time there were fewer trees falling all over the power system.

Lysis, there is a means by which you can see higher inland gusts, but it's not really friction. Where friction saps wind speed compared to being over water, the loss of the mechanism to maintain the hurricane (the warm waters & moisture off of the ocean) also leads to a greater susceptibility for downdrafts to form.

Primarily, these things can form with the introduction of dry air into the midlevels of the column, where evaporative cooling from precipitation leads to an increased susceptibility for downdrafts as the convection dies out within the storm. In the tropics, the moisture and heating that is carried upward by convective updrafts helps to maintain the atmosphere in a state not to allow this to happen, maintaining the convection and updrafts and leading to a feedback cycle upon which the storm may grow. (As an aside, note that it is not the convection that drives the storm, but it is the updrafts from the convection which provide a conduit for the moisture and energy to be transported aloft and drive the storm.)

In summary, higher winds are felt at the low-levels off-shore as a result of a strong, well-defined circulation...upon landfall, this begins to be impacted at the lower levels first, resulting in lower overall winds speeds, but the landfall also results in the decay of the convection, by which high winds still present above the boundary layer (about 5000ft up) not impacted by friction may be transported down to the surface. After this point, the winds aloft begin to die off with the overall circulation as it spins down over land.

Had a few responses already to this, but here's my thoughts: A is primarily just convection firing up in response to divergent winds aloft on the SE side of an upper-level trough. B is the focus for the next possible TD, while C bears some watching down the road but is too far east and not well-enough organized to be too concerned with yet.

First of all, I think we have to breathe an enormous sigh of relief that Dennis weakened. Come to think of it, it seems like alot of storms weaken when they get to the northern gulf of Mexico.

In other news, the Atlantic basin believes that it is late August, as (according to NRL) the wave in the central atlantic has become TD5. This may or may not be true, but my hunch is that it actually is true.

Probably wont deepen too quickly, but going over progressively warmer waters, so it should strengthen

Max Mayfield was just Live on CNN and said they will likely be issuing advisories on TD 5 tonight (11pm). Although he did forget what the name of the system would be once it attains Tropical Storm Strength, someone off set reminded him.

By the way, good job to folks at NHC who nailed the track of this system, and the other mets at CHFC.

Forum Permissions
You cannot start new topics
You cannot reply to topics
HTML is disabled
UBBCode is enabled

Rating:
Topic views: 14340

Rate this topic

Jump to

Note: This is NOT an official page. It is run by weather hobbyists and should not be used as a replacement for official sources.
CFHC's main servers are currently located at Hostdime.com in Orlando, FL.
Image Server Network thanks to Mike Potts and Amazon Web Services. If you have static file hosting space that allows dns aliasing contact us to help out! Some Maps Provided by:
Great thanks to all who donated and everyone who uses the site as well.
Site designed for 800x600+ resolution
When in doubt, take the word of the National Hurricane Center